Variable damping means

ABSTRACT

A variable damping means for cushioning a vehicle occupant from shocks and vibrations transmitted through the vehicle chassis. The occupant support is allowed to oscillate with low damping to provide maximum isolation for the occupant from light vibrations. In addition, the occupant is cushioned with respect to severe shocks by increased damping. The damping characteristics are changed automatically as the character of the shocks and vibrations changes.

United States Patent Garth 0. Hall; Harvey N. Tengler, both 01 New Berlin, Wis.

Inventors Appl. No. 38,275 Filed May 18, 1970 Patented Jan. 4, 1972 Assignee Universal Oil Products Company Des Plaines, Ill.

VARIABLE DAMPING MEANS 15 Claims, 11 Drawing Figs.

US. Cl. 248/400, 188/285, 267/117, 267/131, 297/345 Int. Cl. B60n 1/02 Field of Search 243/400, 399, 372, 378, 157; 267/131, 117; 188/285, 299; 297/345; 280/124 F [56] References Cited UNITED STATES PATENTS 2,032,124 2/ 1936 Funston 188/299 X 3,040,841 6/1962 Schultze 188/299 3,215,386 1 1/1965 Swenson 248/400 3,227,466 1/ 1966 Garcea et al.... 280/ 124 F X 3,275,277 9/ 1966 lllar et a1 188/299 X 3,300,203 1/ 1967 Carter et al 267/ 1 17 Primary Examiner-J. Franklin Foss Attorneys-James R. Hoatson, Jr. and Philip T. Liggett ABSTRACT: A variable damping means for cushioning a vehicle occupant from shocks and vibrations transmitted through the vehicle chassis. The occupant support is allowed to oscillate with low damping to provide maximum isolation for the occupant from light vibrations. in addition, the occupant is cushioned with respect to severe shocks by increased damping. The damping characteristics are changed automatically as the character of the shocks and vibrations changes.

PATENTED JAN 4 972 SHEET 1 [IF 4 Figure & m M R Y I E TMT 5 Mi y VOYQJT b r l A L 2 id x 5 PATENTEDJAN 4mm 3,632,071

SHEET 2 OF 4 58'VOK //v VENTORS" Garth 0. Hall BK Harvey IV. Tang/er VARIABLE DAMPING MEANS A variable damping means for cushioning a vehicle occupant from shocks and vibrations transmitted through the vehicle chassis. The occupant support is allowed to oscillate with low damping to protect the occupant from light vibrations. In addition, the occupant is cushioned with respect to severe shocks by increased damping. The damping characteristics are changed automatically as the character of the shocks and vibrations changes.

This invention is normally used as part of a seat suspension for the driver of a heavyduty vehicle, although it is appropriate for use with any vehicle which subjects the operator to vibration. The occupant support which is cushioned is normally the support for the driver or operator of the vehicle, though the invention may similarly be used to enhance the comfort of other occupants of the vehicle. The invention is directed both toward use in the suspension of vehicle seats and for use in suspending an operator cab or other occupant compartments of a vehicle.

In conventional vehicle seat or cab suspensions, the occupant support of a vehicle is normally biased away from the vehicle frame through the use of conventional spring means, including air cushions, airoil suspension systems, and the like. These spring means cause the occupant to undergo oscillation as the vehicle is subjected to shocks and vibrations while traveling on a road, track, or over other terrain. Since conditions can occur which cause the oscillation of the occupant support to exceed the vehicle oscillation, the occupant suspension systems are frequently augmented with damping devices to reduce the amplitude of oscillation to which the occupant is subjected. The conventional damping devices are normally comprised-of single or multiple shock absorbers having fixed damping characteristics. Shock absorbers having the most desirable damping characteristics are positioned between the vehicle frame and the occupant support so as to allow a slight amount of oscillation and yet dampen extremely hard jolts to which the vehicle is subjected. This optimizing arrangement using damping devices having fixed damping characteristics is far from satisfactory, however, particularly in vehicles which sometimes operate on smooth roads and at other times operate in rough terrain. Instead of providing optimum comfort under such conditions, these damping devices subject the vehicle occupant to a rather hard ride on smooth surfaces and still provide inadequate control of oscillations at large amplitudes when the vehicle is traveling over rough ter' rain. To solve this problem, several attempts have been made to produce a seat suspension having variable damping, but no workable system of automatic variable damping has yet been achieved.

It is an object of this invention to provide completely automatic variable damping in a vehicle occupant suspension system. The change in damping characteristics is automatic whether the damping is being changed from light to heavy cushioning or whether it is being changed from heavy to light cushioning. The purpose of providing variable damping in a vehicle occupant suspension system is to reduce the amplitude of oscillation of the occupant support when the vehicle undergoes severe shocks but to do so without creating a hard ride for the vehicle occupant when the vehicle is subjected to light vibrations.

It is another object of this invention to provide a wide range of adjustments to both the heavy and light damping or shock absorbing characteristics of the variable damping system. The damping characteristics may be made to vary continuously throughout the operation of the vehicle, but preferably are changed only when the vehicle is subjected to extreme shocks. The damping characteristics of this invention may be made adjustable so as to be suitable for any vehicle, regardless of the conditions under which it operates.

Yet another object of the invention is to produce a variable damping system having maintenance free components so as to minimize damage to the damping system and so as to minimize the routine maintenance required. Unless there is an equipment failure, no replenishment of fluids nor exchange of parts in the system is required.

Still another object of the invention is to produce a variable damping system which is operable from existing hydraulic or pneumatic systems in a vehicle having such internal systems. This invention may be operated from these internal systems, though its use is not restricted to vehicles having such internal systems.

In one broad aspect, the invention is a variable clamping device for use in hydraulically cushioning a vehicle occupant comprising: a vehicle frame; an occupant support vertically movable with respect to said vehicle frame; a first hydraulic cylinder interposed between said vehicle frame and said occupant support; a closable valve connected by a fluid transfer line to said first hydraulic cylinder; a pressurized hydraulic fluid reservoir connected to said closable valve, thereby providing a passageway closable by said closable valve between said first hydraulic cylinder and said hydraulic fluid reservoir; a flow regulating link operably connected to said closable valve and operable by movements of said occupant support, whereby said link moves and operates said closable valve when said occupant support moves in at least one direction; a second hydraulic cylinder interposed between said flow regulating link and either said occupant support or said vehicle frame; a hydraulic fluid line leading from said second hydraulic cylinder; a constrictive valve connected to said hydraulic fluid line; a check valve connected to said hydraulic fluid line in parallel with said constrictive valve, whereby said check valve allows hydraulic fluid to flow in one direction with respect to said hydraulic cylinder; and a pressurized hydraulic fluid reservoir connected to said constrictive valve and to said check valve.

In another broad aspect, this invention is a variable damping device for use in hydraulically cushioning a vehicle occupant comprising: a vehicle frame; an occupant support vertically movable with respect to said vehicle frame; a hydraulic cylinder interposed between said vehicle frame and said occupant support; a valve housing containing a passageway therethrough and a blocking valve located in said passageway and connected to said hydraulic cylinder by a fluid transfer line; a pressurized hydraulic fluid reservoir in communication with said passageway; a barrier panel with respect to which said valve housing is relatively movable, and said barrier panel is located in said hydraulic fluid reservoir transverse to the direction of relative motion of said valve housing, whereby relative movement of said valve housing causes movement of said hydraulic fluid in said hydraulic fluid reservoir and said barrier panel restricts the movement of said hydraulic fluid; a check valve that spans said barrier panel and allows easy passage of hydraulic fluid in one direction while opposing passage of the hydraulic fluid in the opposite direction; and flow regulating linkage connected to said occupant support and operably connected with a relatively large minimum clearance to said valve housing, whereby movement of said occupant support operates said blocking valve only after said linkage moves beyond the limit of said minimum clearance.

In one form of the invention, the damping characteristics, in addition to being variable, may also be adjustable. Adjustment of the damping characteristics may be made in a number of ways, but is most easily accomplished where the closable valve is adjustable or where the constrictive valve is adjustable in those forms of the invention employing closable or constrictive valves. In those forms of the invention in which an actuating arm and a flow regulating link are employed in lieu of a flow regulating linkage connected to a valve housing, the position in the cycle of oscillation at which the damping characteristics begin to vary may be changed or adjusted by varying the manner in which movements of the occupant support operate the flow regulating link. In one construction, an actuating arm is attached to the occupant support and is engageable with the flow regulating link, whereby the actuating arm engages the link and causes the link to move when the occupant support moves in at least one direction. The flow regulating link and the actuating arm may be engaged throughout the oscillation of the occupant support, in which case damping is continuously varied. Alternatively, the actuating an'n may be constructed so as to engage a flow regulating link when the occupant support reaches a predetermined point in either the upper or lower portion of an oscillatory cycle of the occupant support with respect to the vehicle frame. In another arrangement, one portion of the flow regulating link may be biased toward the occupant support. When contact is established between that portion of the flow regulating link and the occupant support, the continued movement of the occupant support in its oscillatory cycle will cause the flow regulating link to operate the closable valve. Whether or not continuous operation of the closable valve exists depends upon whether or not the biased portion of the flow regulating link establishes continuous contact with the occupant support or whether contact is established only during a portion of the oscillatory cycle.

In those forms of the invention employing a flow regulating linkage connected with a relatively large minimum clearance to a valve housing, the position in the cycle of oscillation at which the damping characteristics begin to vary may be changed or adjusted by varying the minimum clearance provided between the flow regulating linkage and the valve housmg.

The features of several embodiments of this invention are more clearly illustrated in the accompanying drawings in which:

FIG. 1 is a front elevational view in partial section of an embodiment of this invention employed with a vehicle seat.

FIG. 2 is a side elevational view of isolated components taken along the lines 22 of FIG. 1.

FIG. 3 is a side elevational view of a modification of some of the components of FIG. 1.

FIG. 4 is a partial elevational view of a modification of FIG. 1.

FIG. 5 is a front elevational view in partial section of another embodiment of this invention employed with a supported vehicle cab.

FIG. 6 is a sectional view taken along the lines 66 of FIG. 5.

FIG. 7 is a sectional view taken along the lines 77 of FIG. 5.

FIG. 8 illustrates an alternative embodiment of the flow regulating linkage and valve housing of FIG. 5.

FIG. 9 illustrates an alternative embodiment of the flow regulating linkage and valve housing of FIG. 5.

FIG. 10 is a sectional view taken along the lines l0l0 of FIG. 9.

FIG. 11 is another alternative embodiment of the flow regulating linkage and the valve housing of FIG. 5.

Referring now to FIG. 1 there is shown a seat 4 having a seat pan 6 which supports a seat cushion 5. Seat 4 serves as an occupant support which is vertically movable with respect to vehicle frame 2. Welded to vehicle frame 2 are support angles 3 which extend upward toward seat 4. At the forward, or highest portions of support angles 3 are welded lateral U- shaped brackets 37. Sloping downward from front to rear and welded to support angles 3 are guide or track sections 10. Extending downward from seat pan 6 are seat support brackets 7. Seat support brackets 7 extend fore and aft along seat pan 6 and increase in height from the front to the rear of the seat. As a result, the extreme downward extremities of seat support brackets 7 are at the rear of the seat whilethe shortest vertical dimensions are at the front of the seat. This isjust opposite the construction of support angles 3. Welded to seat support brackets 7 are guide or track sections 11, which slope downward from front to rear at a slope less extreme than that of track sections 10.

The type of seat suspension depicted in FIG. 1 is a form of a scissors suspension, which is quite common in the field of vehicle seating. The scissors arms on each side of the vehicle seat include an arm 8 sharply pitched downward and to the rear, and an arm 9 pitched downward and to the rear but at a less extreme slope than arm 8. The front (upper) ends of arms 8 are pivotally fastened to seat support brackets 7. To the lower ends of arms 8 are pivotally attached rollers which travel within the confines of track sections 10. Similarly, the upper ends of arms 9 are pivotally attached to U- shaped brackets 37 while rollers pivotally attached to the lower ends of arms 9 travel within the confines of track sections 11. The upper arm 8 and the lower arm 9 on each side of the seat are pivotally fastened together near their midsections by bolt means 45.

As the vehicle travels over a surface, the seat occupant is insulated from jolts and vibrations by the clamping device of this invention. To cushion the seat occupant, the seat 4 undergoes periodic oscillation with respect to vehicle frame 2. As the seat 4 approaches vehicle frame 2 in the downward portion of its cycle of oscillation, the slope difference between arms 8 and 9 decreases as the arms 8 and 9 pivot with respect to each other about bolt means 45 The rollers attached to the ends of the arms travel downward and to the rear in their respective track sections. As seat 4 begins moving upward with respect to vehicle frame 2, the slope difierence of arms 8 and 9 increases as the arms pivot with respect to each other about bolt means 45 and the rollers attached to the lower ends of arms 8 and 9 move upward and to the front in their respective track sections. At the extreme upper position of the cycle of oscillation, the direction of relative rotation of the arms 8 and 9 with respect to each other again changes, and the oscillation cycle repeats itself continuously at a diminished amplitude in response to a given jolt or vibration.

The damping device of this invention serves to diminish the amplitude of oscillation rapidly yet cushion the seat occupant sufficiently during the travel of the vehicle. The spring and damping device of this embodiment, in addition to vehicle frame 2 and seat 4, includes a first hydraulic cylinder 12, a closable valve 14, a pressurized hydraulic fluid reservoir 18, a flow regulating link 29, and actuating arm 24, a second hydraulic cylinder 31, a hydraulic fluid line 32, a constrictive valve 34, a check valve 33, and a second pressurized hydraulic fluid reservoir 36. The first hydraulic cylinder 12 is interposed between vehicle frame 2 and seat 4. The piston arm of hydraulic cylinder 12 is attached to the underside of seat pan 6 while the cylinder portion of hydraulic cylinder 12 is attached by brackets to the vehicle frame 2. Closable valve 14 is connected to hydraulic cylinder 12 by a fluid transfer line 13. The closable valve 14 is shown in partial section in FIG. 1 and is comprised of a cylinder member 15 having an interior radial port 46 and a second port 47. Port 47 could be a second radial port if it were to emerge from beyond sleeve member 20, but in the construction of the embodiment of FIG. 1 port 47 is illustrated as being an axial port connected to radial port 46 by a passageway 61. Closable valve 14 is additionally comprised of a sleeve member 20 having a radial port 17 alignable with the interior radial port 46 of cylinder member 15. Sleeve member 20 is rigidly attached to flow regulating link 29 and cylinder member 15 is rotatably movable about sleeve member 20, although the reverse construction could alternatively be used. As can be seen in FIG. 1, cylinder member 15 passes behind the lefthand support angle 3, which slopes sharply downward and to the rear, and in front of the lefthand support angle 7 and the lefthand scissors arms 8 and 9. Within sleeve member 20just beyond the face of cylinder member 15 is attached an annular ring 48. Annular ring 48 provides an obstruction for the rigid end 49 of inflatable bag 19, so that neither rigid end 49, nor any other part of bag 19, can extend beyond the annular ring 48 toward cylinder member 15. Bag 19 is an inflatable bag attached to the walls of sleeve member 20 at the end of sleeve member 20 opposite rigid end 49. A pneumatic line 22 is connected from this other end of sleeve member 20 to a vessel 23 containing compressed nitrogen. Gas may be added to or withdrawn from vessel 23 by way of valve 62. By virtue of the attachment of bag 19 to the interior walls of sleeve member 20, the hollow portion of sleeve member 20 is divided into a pneumatic cavity 21 and a pressurized hydraulic fluid reservoir 18. As the hydraulic fluid pressure in reservoir 18 varies, the bag 19 will expand or contract to equalize the relative pressures between cavity 21 and reservoir 18 by varying the combined volume of vessel 23, line 22, and pneumatic cavity 21. A fluid passageway exists between hydraulic cylinder 12 and hydraulic fluid reservoir 18 by virtue of the connection formed between fluid transfer line 13 and the ports in cylinder member 15. This passageway is closable by the closable valve 14. That is, fluid will not flow between reservoir 18 and hydraulic cylinder 12 unless the ports 46 and 17 of the closable valve 14 are aligned. In addition, flow between reservoir 1% and hydraulic cylinder 12 will exist, but at a restricted rate when the ports 46 and 17 are only partially aligned.

Since cylinder member is welded to the inside surface of flow regulating link 29, flow regulating link 29 is operably connected to closable valve 16. An actuating arm 24 is attached to the seat 4 and is engageable with flow regulating link 29. As can be seen in FIGS. 3 and 2, actuating arm 24 is threaded at its upper end and is fastened by means of fasteners 25 and 26 to the lefthand support angle 7, which extends downward from seat pan 6. Fasteners 25 and 26 are attached in a conventional manner so as to allow the upper end of the lefthand arm 8 to pivot freely about the lateral portion of actuating arm 24, while actuating arm 24 is rigidly attached to support angle 7.

A second hydraulic cylinder 31 is attached to the vehicle frame 2 and is interposed between the flow regulating link 29 and vehicle frame 2. The piston arm 30 of hydraulic cylinder 31 is pivotally attached to flow regulating link 29 by means of a knob 39. The neck of the knob 39 slides freely within the slot 40 so that the piston rod 30 does not bind as the flow regulating link 29 changes position. The actuating arm 24 has a series of holes 38 drilled in its lower end. The lower end of actuating arm 24 is laterally ofiset from flow regulating link 29 so that actuating arm 24 is engageable with flow regulating link 29 only at the hole 38 through which an engaging bolt assembly 28 extends. A hydraulic fluid line 32 leads from the second hydraulic cylinder 31 to two parallel valves. One of the valves is a constrictive or throttling valve 34 connected to the hydraulic line 32. Connected in parallel with constrictive valve 34 is a check valve 33. Check valve 33 allows hydraulic fluid to flow in one direction with respect to hydraulic cylinder 31, and in the embodiment of FIG. 1 check valve 33 allows hydraulic fluid to flow away from hydraulic cylinder 31, but not toward hydraulic cylinder 31. A pressurized hydraulic fluid reservoir 36 is connected to the other ends of the valves 33 and 34 by means of a hydraulic fluid line 35.

The advantages of the invention can best be examined by observing the function of this embodiment throughout a cycle of oscillation. As the vehicle in which this invention is used travels, jolts are incurred by vehicle frame 2 and are transmitted toward the seat occupant in seat 4. The seat occupant is cushioned from these jolts and vibrations by the spring and the damping device of this invention. in the case of an extremely hard jolt of vehicle frame 2, the seat 4 moves downward a relatively large distance with respect to vehicle frame 2. This causes the piston to move downward within hydraulic cylinder 12, thereby forcing hydraulic fluid through fluid transfer line 13 and through ports 17, 46, and 47 of closable valve 14. The hydraulic fluid is forced into reservoir 18, thereby collapsing bag 19.

As the seat 4 continues in its downward path, the upper ends of the scissor arms 8 swing downward and forward so that engaging arm 24 engages flow regulating link 29 along the rear surface 50 of flow regulating link 29 at engaging bolt assembly 28, as depicted in FIG. 2. Since sleeve member 20 of closable valve 14 is welded to the rear edge of the lefthand support angle 3 and is thereby fixed with respect to the frame 2, and since cylinder member 15 is rigidly welded to flow regulating link 29, flow regulating link 29 and cylinder 15 rotate about the axis of sleeve member 20. This rotation is in a clockwise direction as viewed in H6. 2. It is at the point in the downward stroke of the cycle of oscillation where engaging bolt assembly 23 first engages surface 50 of flow regulating link 29 that the damping characteristics of the seat assembly begin to vary. if the jolt is severe enough to carry seat 4 downward past that point, it is desirable that the damping characteristics in the system be increased so as to decrease the amplitude of oscillation from that which would otherwise occur with fixed damping. As the cylinder member 15 begins to rotate clockwise (FIG. 2) with respect to sleeve member 20, the port 46 begins to rotate out of alignment with port 17 in sleeve member 20. This restricts the flow of fluid from the first hydraulic cylinder 12 to the hydraulic fluid reservoir 18 as the seat 4 proceeds in its downward path of oscillation. Eventually, there is no fluid flow from hydraulic cylinder 12 to the reservoir 18 due to the closure of closable valve 14. Because the port 17 rotates out of alignment with port 46, the damping characteristics of the hydraulic cylinder 12 increase. More simply stated, the damping of hydraulic cylinder 12 increases as the seat 4 moves further downward.

The rotation of flow regulating link 29 causes the piston rod 30 to move downward within the second hydraulic cylinder 31. The movement of piston rod 30 begins when actuating arm 24 first engages flow regulating link 29. The movement of piston rod 30 forces hydraulic fluid out of hydraulic cylinder 31 into hydraulic fluid line 32 and through check valve 33 and constrictive valve 34 towards the pressurized hydraulic fluid reservoir 36. Check valve 33 is constructed to allow much easier passage of hydraulic fluid toward the reservoir 36 than is constrictive valve 34. For this reason, almost all of the fluid flowing out of the second hydraulic cylinder 31 through fluid line 32 passes through the check valve 33 towards reservoir 36.

When the seat 4 reaches its lowest position and reverses direction and begins its upward movement during the other half of its cycle of oscillation, it is desirable that the damping not be reduced rapidly but rather that it be maintained at an increased level for a period of time anticipating other severe oscillations which would otherwise contribute to the discomfort of the vehicle operator. It is for this reason that check valve 33 is constructed so that no flow of hydraulic fluid may occur through it from the reservoir 36 to the second hydraulic cylinder 31. instead, all hydraulic fluid flowing from reservoir 36 to hydraulic cylinder 31 must pass at a relatively slow rate through the constrictive valve 34 and the ascension of piston rod 30 is thus controlled. This allows the flow regulating link 29 to slowly and smoothly rotate counterclockwise (P16. 2) and thus maintain increased damping for a time as determined by the flow through constrictive valve 34. As flow regulating link 29 rotates counterclockwise, the ports 46 and 17 of closable valve 1 3 begin to again come into alignment. As the alignment of these ports becomes more perfect, damping decreases and the suspension system regains the original damping characteristic appropriate for a ride over a relatively smooth surface. Because of the controlled delay in the rotation of flow regulating link 29, as the seat 4 continues to ascend, the actuating arm 24 loses contact with the rear surface 51) of flow regulating link 29. The actuating arm 24 does not reengage flow regulating link 29 until after the seat 4 reaches its extreme upper position in its path of oscillation and again undergoes downward movement to below the midpoint of its path of oscillation. if the vibrations to which the vehicle occupant is subjected are small enough, the amplitude of the cycle of oscillation will be small enough so that actuating arm 24 will not engage flow regulating link 29 unless a more severe jolt is encountered. As governed by the weight of the operator and the roughness of the ride likely to be encountered, the constrictive valve 34, the engaging bolt assembly 28, the gas pressure within vessel 23, and the hydraulic fluid pressure within reservoir 36 may be appropriately adjusted in order to optimize the damping characteristics of the system.

Referring now to FIG. 2, it can be seen that for less damping control it is wise to place engaging bolt assembly 28 through one of the upper holes 38 in actuating arm 24, since this will change the ratio of rotation of flow regulating link 29 to the motion of actuating arm 24. To change the rate of return of the seat to the ride position after extreme jolts, the orifice of the constrictive valve may be varied or the pressure within the hydraulic fluid reservoir 36 may be adjusted.

While the actuating arm 24 of this embodiment has been shown to engage the flow regulating link 29 when the occupant support is in the lower portion of the path of oscillation of the seat 4 with respect to the vehicle frame 2, the engagement of the actuating arm with the flow regulating link could be made to occur in the upper portion of the path of oscillation in order to accomplish the same purpose.

FIG. 3 illustrates an alternative embodiment of the actuating arm, the closable valve, and the second hydraulic cylinder of this invention.

FIG. 3 is a front elevational view of these components isolated from the remaining portion of the embodiment of F IG. 1. The modification of FIG. 3 works identically to that of FIGS. 1 and 2 with the following exceptions. The actuating arm 11 1 is not curved but is merely a fastening means and passes directly through the flow regulating link 29'. In FIG. 3, flow regulating link 29' does not rotate during the downward movement of the occupant support, but rather undergoes only translational motion. That is, as the occupant support moves downward, actuating arm 111 forces flow regulating link 29' downward. Closable valve 14' is a needle valve comprised of a needle member connected by a shaft to the end 43 of connecting lever 42, and an orifice member in a housing 113 rigidly connected to support angle 1 12. Support angle 1 12 is rigidly connected to vehicle frame 2. During the downward movement of the occupant support in the lower portion of the oscillatory cycle, the flow regulating link 29 forces connecting joint 41 to pull downward on end 44 of lever 42. Lever 42 passes through an aperture in support angle 112 and is pivoted at its point of contact with angle 1 12. As connecting joint 41 pulls downward on end 44 of lever 42, end 43 of lever 42 is pulled upward thereby pulling the needle valve of this embodiment into the orifice of the closable valve 14. The resulting effect is the same as occurred with the rotational valve of FIGS. 1 and 2. As in the embodiment of FIGS. 1 and 2, hydraulic fluid is forced through a check valve and constrictive valve (not shown) from a second hydraulic cylinder 31'. In the embodiment of FIG. 3, there is no rotational motion of flow regulating link 29'.

FIG. 4 illustrates another variation of this invention. FIG. 4 is an isolated front view of a portion of a seat 16 vertically movable with respect to vehicle frame 64. The operation and manner of connection of the scissors arms of FIG. 4 is identical to that of FIG. 1. In addition, the closable valve 54 is identical to the closable valve 14. All components of the embodiment of FIG. 4 not illustrated are identical to corresponding members of FIG. 1. The flow regulating link 51, however, differs in construction from flow regulating link 29 in FIG. 1. Flow regulating link 51 is comprised of a main central disk portion 67 to which is welded the cylinder member 114 of closable valve 54. Sloping forward and upward at an angle from disk portion 67 there extends a seat engaging portion 60 of flow regulating link 51. This seat engaging portion 60 is biased toward seat 16 by a biasing spring 116. Portion 60 of the flow regulating link 51 is in contact with seat pan 52 during at least a part of the cycle of oscillation. As seat 16 moves downward toward vehicle frame 64 during the cycle of oscillation, portion 60 of the flow regulating link 51 is forced forward and downward, thereby rotating the entire flow regulating link 51. This rotation causes closable valve 54 to operate in the same manner as did valve 14 of FIG. 1. As flow regulating link 51 rotates, a connection link 115, attached to the disk portion 67 of flow regulating valve 51, pulls downward on piston rod 56 of second hydraulic cylinder 55. Hydraulic cylinder 55 is attached to the underside of seat pan 52 of seat 16. Since portion 60 of flow regulating link 51 is in contact with seat pan 52 and is operated by seat pan 52 during the downward portion of the cycle of operation, piston rod 56 moves downward relative to seat 16 and causes hydraulic fluid to be drawn into second hydraulic cylinder 55 as seat 16 moves downward. Hydraulic fluid is drawn from a reservoir through a hydraulic fluid line 57 in which are positioned a constrictive valve 59 and a check valve 58. The positioning of check valve 58 to allow flow into second hydraulic cylinder 55 makes the operation of the damping system correspond to the operation of the embodiment of FIG. 1. Check valve 58 could be positioned so as to allow flow in the opposite direction, in which case the heavy damping would occur during the downward stroke of the cycle of oscillation, rather than the upward stroke as happens in the damping systems of FIGS. 1 and 4. The effect on the seat occupant would be the same.

Referring now to FIG. 5, there is shown an alternative embodiment of this invention. A vehicle cab is vertically movable with respect to a vehicle frame 2 as governed by a suspension system very similar to that of FIG. 1. The elements of the scissors suspension of FIG. 5 include arms 8 and 9', cab support brackets 7, track sections 10' and 11 support angles 3, lateral U-shaped brackets 37', and bolt means 45'. These elements cooperate and perform the same function as do their unprimed equivalents in FIG. 1 except that the pivot points are selected to provide parallel motion. In addition, the embodiment of FIG. 5 is also similar to that of FIG. 1 in that a hydraulic cylinder 12 is interposed between the vehicle frame 2 and the vehicle cab 95.

The spring and damping means of this embodiment of the invention, in addition to the vehicle frame 2', the vehicle cab 95, and the hydraulic cylinder 12, includes a valve housing 68, a pressurized hydraulic fluid reservoir 101, a barrier panel 72, a check valve 71, and flow regulating linkage that is operably connected to the valve housing 68. The valve housing 68 is connected to hydraulic cylinder 12 by a fluid transfer line 13'. Valve housing 68 is shown in partial section in FIG. 5 and contains a passageway 69 extending therethrough and a blocking valve located in the passageway 69 and connected to the hydraulic cylinder 12 by fluid transfer line 13'. The blocking valve of this embodiment may be considered to be the interface between the port located at the end of passageway 69 in valve housing 68, and the aperture 65 where the fluid transfer line 113 communicates with the interior of a cylindrical sleeve member 66 welded to the left-hand support angle 3. Relative rotation of the valve housing 68 with respect to sleeve member 66 causes the port 100 and the aperture 65 to come into alignment or to shift from an aligned position. When the port 100 and the aperture 65 are aligned, hydraulic fluid may flow freely from the hydraulic cylinder 12 to the hydraulic fluid reservoir 101. When the valve housing 68 shifts with respect to the sleeve member 66, thereby moving the port 100 and the aperture 65 out of alignment, no fluid may flow through the port 100 or the aperture 65 because valve housing 68 fits closely within sleeve member 66 thereby sealing the port 100 and the aperture 65. At the other end of passageway 69 in valve housing 68 is located a port 106 in communication with hydraulic fluid reservoir 101.

Within sleeve member 66 just beyond valve housing 68 there is located a transverse separation panel '70 with a passageway 74 therethrough. Transverse separation panel 70 is constructed in the form of an annular ring perforated by an offcenter passageway 74 that provides an obstruction for the rigid end 107 of inflatable bag 19, so that neither rigid end 107, nor any other part of bag 19', can extend beyond the transverse separation panel 70 toward valve housing 68. Bag 19' is an inflatable bag attached to the walls of sleeve member 66 to the right of rigid end 107. By virtue of the attachment of bag 19' to the interior walls of sleeve member 66, the portion of sleeve member 66 to the right of valve housing 68 is divided into a pneumatic cavity 75 and pressurized hydraulic fluid reservoir 101. As the hydraulic fluid pressure in reservoir 101 varies, bag 19' will expand or contract to equalize the relative pressures between cavity 75 and reservoir 10] by varying the volume of the pneumatic cavity 75. Air or other gas may be added to or withdrawn from the pneumatic cavity 75 through a pneumatic valve 76.

The valve housing 68 has a cylindrical central portion 110 and two end portions. One of the end portions, end portion 108, is of a segmental cross section slightly only smaller than a semicircle having the same common radius. The cross section of end portion 108 is best illustrated in FIG. 7.

The barrier panel 72 is located in the hydraulic fluid reservoir 101 transverse to the direction of relative motion of the valve housing 68. Barrier panel 72 is a planar rectangle radially extending from the axis of the sleeve member 66 to the inner surface of the sleeve member 66 coextensive with and positioned generally opposite the first segmental end portion 108 of valve housing 68 and intersecting and welded to transverse separation panel 70 within the sleeve member 66. Due to the geometry of the end portion 108 and the barrier panel 72, it can be seen that the valve housing 68 is relatively movable with respect to the barrier panel 72, and that relative movement of the valve housing 68 causes movement of the hydraulic fluid in the hydraulic fluid reservoir 101. It can also be seen that the barrier panel 72 restricts the movement of this hydraulic fluid. It can be seen from FIG. 7 that when the valve housing 68 (including the end portion 108) rotates counterclockwise, hydraulic fluid is forced from the lower lefthand portion of the fluid reservoir 101 to the lower righthand portion of the fluid reservoir 101. The only path available through which the hydraulic fluid can flow is through the channel between the end portion 108 and the barrier panel 72. This channel is centrally located with respect to the sleeve member 66. The hydraulic fluid cannot flow around the barrier panel 72 because one end of barrier panel 72 abuts and is welded to the transverse separation panel 70 while the other end of barrier panel 72 terminates very close to the central portion 110 of valve housing 68. A rubber gasket or other seal may be used at this junction. Similarly, the face of end portion 108 is also located immediately adjacent the transverse separation panel 70. The viscosity of the hydraulic fluid as it moves through the channel between the end portion 108 and the barrier panel 72 causes a great deal of resistance to the counterclockwise rotation of the valve housing 68. The same is not true, however, when the valve housing 68 rotates clockwise This is because a check valve 71 is located in the barrier panel 72 and allows easy passage of the hydraulic fluid from the righthand side of the panel to the lefthand side of the panel while opposing passage of the hydraulic fluid from the lefthand side of the panel to the righthand side of the panel. While the check valve 71 could be located in an external line entering and leaving the sleeve member 66, it is more conveniently located in an opening 79 extending transversely through the barrier panel 72.

The other or second end portion of 109 of the valve housing 68 is also of a segmental cross section only slightly smaller than a semicircle having the same radius. The outer boundaries of the cross section of end portion 109 is, but need not be, identical to the outer boundaries of the cross section of end portion 108, and is so illustrated in FIG. 6. The flow regulating linkage is comprised of an actuating arm 24 threaded at its upper end and fastened by means of fasteners 25' and 26' to the lefthand cab support angle 7', which extends downward from cab 95. The fasteners 25 and 26 rigidly fasten the lateral portion of the actuating arm 24 to the cab support angle 7. The lower end of the actuating arm 24' is pivotally fastened to a torsion arm 117 by a pivot pin assembly 118. The torsion arm 117 is rigidly fastened to an engaging cylinder 119 which extends axially into the sleeve member 66. The engaging cylinder 119 has an end 80 adjacent to the end portion 109 of the valve housing 68. Adjacent end 80 is of segmental cross section only slightly smaller than a semicircle having the same radius and is located in sleeve member 66 generally opposite the second end portion 109 of valve housing 68, as indicated in FIG. 6. The flow regulating linkage is thereby connected to the occupant support (vehicle cab 95) and is operably connected with a relatively large minimum clearance to the valve housing 68. The minimum clearance is formed by the distance between the upper surface 77 of adjacent end 80 of the actuating cylinder 119 and the lower surface 78 of the end portion 109 of the valve housing 68. It can be seen that valve housing 68 will be rotated only after adjacent end 80 is rotated moves beyond the limits of the relatively large minimum clearance and after the edge of surface 77 makes contact with the edge of surface 78.

The minimum between the flow the regulating linkage and the valve housing 68 may take a number of different forms. One such variation is illustrated in FIG. 8 in which the second end portion of a valve housing and an adjacent end 83 of the flow regulating linkage are axially aligned within the sleeve member 66 and are connected by an axially extending torsion bar 87. A rotation of the adjacent end 83 of the flow regulating linkage will have no effect on the valve housing 85 until enough torsion is applied to torsion bar 87 to overcome the friction of valve housing 85 with respect to sleeve member 66. When this torsional force is reached, the valve housing 85 will begin to rotate port 81 with respect to the fluid transfer line 13'. The same result is achieved in the modification of FIG. 9. In FIG. 9 the second end portion of the valve housing 86 has a circular surface and an adjacent end 84 of the flow regulating linkage is coaxial with the valve housing 86 and has a circular surface. One of the aforesaid circular surfaces, in this case the surface of the end portion of the valve housing 86, has at least one and preferably two tracks extending in arcs about the axis of the valve housing 86. These tracks take the form of grooves that are shallow at one end and deep at the other end in the circular surface of valve housing 86. The deep ends 91 and 92 of the grooves are each located at the clockwise extremities of the grooves as depicted in FIG. 10. The deep ends 91 and 92 of the grooves are abruptly terminated by an obstacle, which in the embodiment illustrated is merely comprised of the structural material of the valve housing 86. The shallow ends 93 and 94 of the grooves smoothly blend into the circular surface of the second end portion of the valve housing 86. Guide followers 88 protrude from the other circular face, the circular surface of the adjacent end 84 of the flow regulating link age. These guide followers are axially movable within the longitudinal wells and are biased toward the circular surface of the end portion of the valve housing 86 by springs 89. The guide followers 88 engage the grooves in the face of the end portion of the valve housing 86 so that relative rotation of the end 84 of the flow regulating linkage with respect to the valve housing 86 creates an operable connection between the flow regulating linkage and the blocking valve only when the rotation of the guide followers is resisted by the structural material of the valve housing 86 at the deep ends 91 and 92 of the grooves. The arcuate travel of the guide followers within the grooves provides the minimum clearance before engagement of valve housing 86 and adjacent end 84 of the flow regulating linkage in this modification of the invention.

The minimum clearance is provided in yet another form in the modification of FIG. 11. In this modification the second end portion of the valve housing 102 and an adjacent end 103 of the flow regulating linkage are axially aligned within the sleeve member 66. The second end of the valve housing 102 terminates in an elliptical face 105. Similarly, the adjacent end 103 of the flow regulating linkage terminates in an elliptical face 104. Elliptical faces 104 and 105 are parallel and separated slightly from each other, the slight separation creating the minimum clearance. That is, the end 103 of the flow regulating linkage must rotate a slight distance before contact is established with the valve housing 102. It is only after this initial contact is made that the port 82 is rotated with respect to the fluid transfer line 13.

Returning to the embodiment of FIG. 5, it can be seen that the operation of the embodiment of FIG. 5 is very similar to that of FIG. 1. At the beginning of a cycle of oscillation, the blocking valve is open as the port 100 and the aperture 65 are fully aligned. As the cab moves downward in the downward portion of the cycle of oscillation, the actuating arm 24 rotates the torsion arm 117 thereby rotating the actuating cylinder 119. This rotation has no effect on the valve housing until the edges of the surfaces 77 and 78 contact each other. When this contact is established, the valve housing 68 begins to rotate and the port 160 begins to move out of, alignment with port 65. Prior to the contact of surfaces 77 and 78, fluid is easily forced through the fluid transfer line 13, through the blocking valve, and through the passageway v69 into the hydraulic fluid reservoir The damping characteristics of the system during this early portion of the cycle of oscillation are quite small since the path and flow of the hydraulic fluid offers little resistance. As the cab 95 continues to move downward, however, and as the port 100 begins to move out of alignment with the port 65, the fluid flow from the hydraulic cylinder 12 to the hydraulic fluid reservoir 101 diminishes thereby increasing the damping characteristics of the system. The rotation of the valve housing 68 is not resisted by the viscosity of the fluid in the hydraulic fluid reservoir 101 because the fluid readily passes through the check valve 71 in the barrier panel 72 as the valve housing 68 rotates clockwise. At the lowest position of the vehicle cab 95, the blocking valve is completely closed. As the vehicle cab 95 begins to rise, the damping characteristics of the system are increased by the resistance of the hydraulic fluid within the hydraulic fluid reservoir 101. That is, the counterclockwise rotation of valve housing 68 by the flow regulating linkage is resisted by the viscosity of the hydraulic fluid within the hydraulic fluid reservoir 101. As the valve housing 68 attempts to rotate counterclockwise, the check valve 71 opposes flow through the opening 79,

thereby limiting the allowable path of flow to the channel formed between the surface of the first end 108 and the barrier panel 72. Because this channel is so narrow, the cab is allowed to rise only at a rather slow rate even after the port 100 comes into alignment with the port 65 and fluid may freely flow from the hydraulic fluid reservoir 101 into the hydraulic cylinder 12. The resulting increased damping characteristics of the system exist until the cab 95 reaches its uppermost position in the cycle of oscillation. The retention of these high damping characteristics for a time is desirable because of the likelihood of further extreme jolts such as that which caused the original cycle of oscillation in the first place.

During the smooth ride condition, the actuating cylinder 119 oscillates in rotation only slightly within the sleeve member 66. This slight oscillation is normally within the minimum clearance allowed by the system so that the damping characteristics are not changed during the level ride condition, but only increase when the vehicle is subjected to extreme shocks or vibrations.

As will be obvious to those skilled in the field of vehicle occupant seating, numerous mechanical equivalents may be provided in place of those specifically enumerated in the embodiments of this invention. For this reason, the foregoing description and illustrations of the mechanical components of this invention are for purposes of illustration only, as the interaction of these components in the manner claimed is considered to be the invention disclosed herein.

We claim as our invention:

1. A variable damping device for use in hydraulically cushioning a vehicle occupant comprising:

a. a vehicle frame,

b. an occupant support vertically movable with respect to said vehicle frame,

c. a first hydraulic cylinder interposed between said vehicle frame and said occupant support,

a closable valve connected by a fluid transfer line to said first hydraulic cylinder,

e. a pressurized hydraulic fluid reservoir connected to said closable valve, thereby providing a passageway closable by said closable valve between said first hydraulic cylinder and said hydraulic fluid reservoir,

f. a flow regulating link operably connected to said closable valve and operable by movements of sad occupant support, whereby said link moves and operates said closable valve when said occupant support moves in at least one direction,

g. a second hydraulic cylinder interposed between said How regulating link and said vehicle frame,

h. a hydraulic fluid line leading from said second hydraulic cylinder,

i. a constrictive valve connected to said hydraulic fluid line,

j. a check valve connected to said hydraulic fluid line in parallel with said constrictive valve, whereby said check valve allows hydraulic fluid to flow in one direction with respect to said hydraulic cylinder, and

k. a pressurized hydraulic fluid reservoir connected to said constrictive valve and to said check valve.

2. The variable damping device of claim 1 further characterized in that said constrictive valve is an adjustable valve.

3. The variable damping device of claim 1 further characterized in that an actuating arm is attached to said occupant support and is engageable with said flow regulating link, whereby said arm engages said link and causes said link to move when said occupant support moves in at least one direction.

4. The variable damping device of claim 3 further characterized in that said actuating arm causes said flow regulating link to rotate when said occupant support moves down ward.

5. The variable damping device of claim 4 further characterized in that said closable valve is comprised of a cylinder member having an interior radial port, a second port, and a passageway therebetween, and a sleeve member having a radial port alignable with said interior radial port of said cylinder member, and one of the aforesaid members is rigidly attached to said flow regulating link.

6. The variable damping device of claim 3 further characterized in that said closable valve is a needle valve comprised of a needle member and an orifice member, and one of said members is operably connected to said flow regulating link and the other of said members is fixed relative to said vehicle frame.

7. The variable damping device of claim 3 further characterized in that said actuating arm engages said flow regulating link when said occupant support is in the lower portion of an oscillatory cycle with respect to said vehicle frame.

8. A variable damping device for use in hydraulically cushioning a vehicle occupant comprising:

a. a vehicle frame,

b. an occupant support vertically movable with respect to said vehicle frame,

c. a first hydraulic cylinder interposed between said vehicle frame and said occupant support,

d. a closable valve connected by a fluid transfer line to said first hydraulic cylinder,

e. a pressurized hydraulic fluid reservoir connected to said closable valve, thereby providing a passageway closable by said closable valve between said first hydraulic cylinder and said hydraulic fluid reservoir,

f. a flow regulating link operably connected to said closable valve and operable by movements of said occupant sup port, whereby said link moves and operates said closable valve when said occupant support moves in at least one direction,

g. a second hydraulic cylinder interposed between said flow regulating link and said occupant support,

h. a hydraulic fluid line leading from said second hydraulic cylinder,

i. a constrictive valve connected to said hydraulic fluid line,

j. a check valve connected to said hydraulic fluid line in parallel with said constrictive valve, whereby said check valve allows hydraulic fluid to flow in one direction with respect to said hydraulic cylinder, and

k. a pressurized hydraulic fluid reservoir connected to said constrictive valve and to said check valve.

9. A variable damping device for use in hydraulically cushioning a vehicle occupant comprising:

a. a vehicle frame,

b. an occupant support vertically movable with respect f0 said vehicle frame,

c. a hydraulic cylinder interposed between said vehicle frame and said occupant support,

d. a valve housing containing a passageway therethrough and a blocking valve located in said passageway and connected to said hydraulic cylinder by a fluid transfer line,

e. a pressurized hydraulic fluid reservoir in communication with said passageway,

a barrier panel with respect to which said valve housing is relatively movable, and said barrier panel is located in said hydraulic fluid reservoir transverse to the direction of relative motion of said valve housing, whereby relative movement of said valve housing causes movement of said hydraulic fluid in said hydraulic fluid reservoir and said barrier panel restricts the movement of said hydraulic fluid,

g. a check valve that spans said barrier panel and allows easy passage of hydraulic fluid in one direction while opposing passage of hydraulic fluid in the opposite direction, and

. flow regulating linkage connected to said occupant support and operably connected with a relatively large minimum clearance to said valve housing, whereby movement of said occupant support operates said blocking valve only after said linkage moves beyond the limit of said minimum clearance.

10. The variable damping device of claim 9 further characterized in that there is an opening extending transversely through said barrier panel and said check valve is located in said opening.

11. The variable damping device of claim 10 further characterized in that said valve housing and said hydraulic fluid reservoir are confined within a cylindrical sleeve member, and said valve housing has a cylindrical central portion and at least one end portion of segmental cross section only slightly smaller than a semicircle having the same radius, and a transverse separation panel with a passageway therethrough is located adjacent a first segmental end portion of said valve housing in said hydraulic fluid reservoir, and said barrier panel is a planar rectangle radially extending from the axis of said sleeve member to the inner surface of said sleeve member coextensive with and positioned generally opposite said first segmental end portion of said valve housing and intersecting said transverse separation panel within said sleeve member.

12. The variable damping device of claim 11 further characterized in that a second end portion of said valve housing is of segmental cross section only slightly smaller than a semicircle having the same radius, and an adjacent end of said flow regulating linkage is of segmental cross section only slightly smaller than a semicircle having the same radius and is located in said sleeve member generally opposite said second end portion of said valve housing, thereby creating the aforesaid minimum clearance between said valve housing and said flow regulating linkage.

13. The variable damping device of claim 11 further characterized in that a second end of said valve housing has a circular surface and an adjacent end of said flow regulating linkage is coaxial with said valve housing and has a circular surface, and a first of the aforesaid circular surfaces has at least one track extending in an arc about the axis of said valve housing abruptly terminated by an obstacle at one end and smoothly blending into said first circular surface at the other end, and at least one guide follower protrudes from a second of the aforesaid circular surfaces and is spring biased toward said first of the aforesaid circular surfaces and engages said track, whereby relative rotation of said adjacent end of said flow regulating linkage with respect to said valve housing creates an operable connection between said flow regulating linkage and said blocking valve only when rotation of said guide follower is resisted by said obstruction.

14. The variable clamping device of claim 11 further characterized in that a second end of said valve housing and an adjacent end of said flow regulating linkage are axially aligned and are connected b an axially extending torsion bar.

15. The variable amping device of claim 11 further characterized in that a second end of said valve housing and an adjacent end of said flow regulating linkage are axially aligned within said sleeve member and terminate in parallel elliptical faces slightly separated from each other, thereby creating said minimum clearance. 

1. A variable damping device for use in hydraulically cushionIng a vehicle occupant comprising: a. a vehicle frame, b. an occupant support vertically movable with respect to said vehicle frame, c. a first hydraulic cylinder interposed between said vehicle frame and said occupant support, d. a closable valve connected by a fluid transfer line to said first hydraulic cylinder, e. a pressurized hydraulic fluid reservoir connected to said closable valve, thereby providing a passageway closable by said closable valve between said first hydraulic cylinder and said hydraulic fluid reservoir, f. a flow regulating link operably connected to said closable valve and operable by movements of sad occupant support, whereby said link moves and operates said closable valve when said occupant support moves in at least one direction, g. a second hydraulic cylinder interposed between said flow regulating link and said vehicle frame, h. a hydraulic fluid line leading from said second hydraulic cylinder, i. a constrictive valve connected to said hydraulic fluid line, j. a check valve connected to said hydraulic fluid line in parallel with said constrictive valve, whereby said check valve allows hydraulic fluid to flow in one direction with respect to said hydraulic cylinder, and k. a pressurized hydraulic fluid reservoir connected to said constrictive valve and to said check valve.
 2. The variable damping device of claim 1 further characterized in that said constrictive valve is an adjustable valve.
 3. The variable damping device of claim 1 further characterized in that an actuating arm is attached to said occupant support and is engageable with said flow regulating link, whereby said arm engages said link and causes said link to move when said occupant support moves in at least one direction.
 4. The variable damping device of claim 3 further characterized in that said actuating arm causes said flow regulating link to rotate when said occupant support moves downward.
 5. The variable damping device of claim 4 further characterized in that said closable valve is comprised of a cylinder member having an interior radial port, a second port, and a passageway therebetween, and a sleeve member having a radial port alignable with said interior radial port of said cylinder member, and one of the aforesaid members is rigidly attached to said flow regulating link.
 6. The variable damping device of claim 3 further characterized in that said closable valve is a needle valve comprised of a needle member and an orifice member, and one of said members is operably connected to said flow regulating link and the other of said members is fixed relative to said vehicle frame.
 7. The variable damping device of claim 3 further characterized in that said actuating arm engages said flow regulating link when said occupant support is in the lower portion of an oscillatory cycle with respect to said vehicle frame.
 8. A variable damping device for use in hydraulically cushioning a vehicle occupant comprising: a. a vehicle frame, b. an occupant support vertically movable with respect to said vehicle frame, c. a first hydraulic cylinder interposed between said vehicle frame and said occupant support, d. a closable valve connected by a fluid transfer line to said first hydraulic cylinder, e. a pressurized hydraulic fluid reservoir connected to said closable valve, thereby providing a passageway closable by said closable valve between said first hydraulic cylinder and said hydraulic fluid reservoir, f. a flow regulating link operably connected to said closable valve and operable by movements of said occupant support, whereby said link moves and operates said closable valve when said occupant support moves in at least one direction, g. a second hydraulic cylinder interposed between said flow regulating link and said occupant support, h. a hydraulic fluid line leading from said second hydraulic cylinder, i. a constrictive valve connected to said hydraulic fluid liNe, j. a check valve connected to said hydraulic fluid line in parallel with said constrictive valve, whereby said check valve allows hydraulic fluid to flow in one direction with respect to said hydraulic cylinder, and k. a pressurized hydraulic fluid reservoir connected to said constrictive valve and to said check valve.
 9. A variable damping device for use in hydraulically cushioning a vehicle occupant comprising: a. a vehicle frame, b. an occupant support vertically movable with respect to said vehicle frame, c. a hydraulic cylinder interposed between said vehicle frame and said occupant support, d. a valve housing containing a passageway therethrough and a blocking valve located in said passageway and connected to said hydraulic cylinder by a fluid transfer line, e. a pressurized hydraulic fluid reservoir in communication with said passageway, f. a barrier panel with respect to which said valve housing is relatively movable, and said barrier panel is located in said hydraulic fluid reservoir transverse to the direction of relative motion of said valve housing, whereby relative movement of said valve housing causes movement of said hydraulic fluid in said hydraulic fluid reservoir and said barrier panel restricts the movement of said hydraulic fluid, g. a check valve that spans said barrier panel and allows easy passage of hydraulic fluid in one direction while opposing passage of hydraulic fluid in the opposite direction, and h. flow regulating linkage connected to said occupant support and operably connected with a relatively large minimum clearance to said valve housing, whereby movement of said occupant support operates said blocking valve only after said linkage moves beyond the limit of said minimum clearance.
 10. The variable damping device of claim 9 further characterized in that there is an opening extending transversely through said barrier panel and said check valve is located in said opening.
 11. The variable damping device of claim 10 further characterized in that said valve housing and said hydraulic fluid reservoir are confined within a cylindrical sleeve member, and said valve housing has a cylindrical central portion and at least one end portion of segmental cross section only slightly smaller than a semicircle having the same radius, and a transverse separation panel with a passageway therethrough is located adjacent a first segmental end portion of said valve housing in said hydraulic fluid reservoir, and said barrier panel is a planar rectangle radially extending from the axis of said sleeve member to the inner surface of said sleeve member coextensive with and positioned generally opposite said first segmental end portion of said valve housing and intersecting said transverse separation panel within said sleeve member.
 12. The variable damping device of claim 11 further characterized in that a second end portion of said valve housing is of segmental cross section only slightly smaller than a semicircle having the same radius, and an adjacent end of said flow regulating linkage is of segmental cross section only slightly smaller than a semicircle having the same radius and is located in said sleeve member generally opposite said second end portion of said valve housing, thereby creating the aforesaid minimum clearance between said valve housing and said flow regulating linkage.
 13. The variable damping device of claim 11 further characterized in that a second end of said valve housing has a circular surface and an adjacent end of said flow regulating linkage is coaxial with said valve housing and has a circular surface, and a first of the aforesaid circular surfaces has at least one track extending in an arc about the axis of said valve housing abruptly terminated by an obstacle at one end and smoothly blending into said first circular surface at the other end, and at least one guide follower protrudes from a second of the aforesaid circular surfaces and is spring biased toward said firsT of the aforesaid circular surfaces and engages said track, whereby relative rotation of said adjacent end of said flow regulating linkage with respect to said valve housing creates an operable connection between said flow regulating linkage and said blocking valve only when rotation of said guide follower is resisted by said obstruction.
 14. The variable damping device of claim 11 further characterized in that a second end of said valve housing and an adjacent end of said flow regulating linkage are axially aligned and are connected by an axially extending torsion bar.
 15. The variable damping device of claim 11 further characterized in that a second end of said valve housing and an adjacent end of said flow regulating linkage are axially aligned within said sleeve member and terminate in parallel elliptical faces slightly separated from each other, thereby creating said minimum clearance. 